Posterior cervical fixation using lateral mass plates has been shown to be a safe and effective method to achieve cervical fusion of adjacent vertebrae. In this technique, a plate is secured posteriorly on two superposed lateral mass plates of adjacent vertebrae typically with a pair of screws each engaging respective lateral mass plates of the two vertebrae, thereby fusing the two vertebrae together. Lateral mass plating is biomechanically superior to laminar wiring or clamping in limiting cervical motion. In addition, unlike posterior laminar wiring or clamping, lateral mass plating does not require the presence of the posterior elements (lamina, spinous process). During the last ten years, posterior plating using lateral mass screw fixation has become more popular for treating instability of the lower cervical spine. Injury to the spinal nerves associated with insertion of lateral mass screws is a complication of this procedure.
Several techniques for lateral screw placement have been developed. Each has its unique entrance point for screw insertion and screw trajectory. Rods connect screws inserted into adjacent vertebrae together. More than one screw (and corresponding multiple vertebrae) may be connected to one rod. Other known techniques for fusing vertebrae include the so-called Mageri technique, the Anderson technique, the An Technique, etc. All of these known techniques involve inserting a screw into a single vertebra.
Known vertebrae connection devices have some drawbacks. They are difficult to contour, and the screw positions are dictated by the fixed plate entry holes. In addition, the screw trajectories are divergent from the plate entry holes, and the connection of the screw to the plate is not rigid. Also, there is no space to pack autograft bone under a screw-plate connection. Screws placed medially or laterally cannot be captured by the plate. Successive screws cannot be compressed or distracted because of the fixed plate hole distances. Moreover, if the plate needs to be revised, the screws must be removed. There is therefore a need for an improved posterior cervical anchoring device.